Molten Salt Corrosion Studies of Sanicro-25 by Electrochemical Techniques at High Temperature

Abstract

Nickel and chromium-based alloys are being considered structural materials for crucibles for electrorefining in pyrochemical reprocessing. LiCl–KCl molten salt is used as an electrolyte under an inert argon atmosphere. In the present work, the corrosion behavior of the Sanicro-25 steel exposed to LiCl–KCl molten salt at 500°C with inert argon cover gas was explored using electrochemical methods like open circuit potential (OCP), linear polarization resistance, and electrochemical impedance spectroscopy (EIS). A change in the OCP of Sanicro-25 towards the noble direction was observed. The linear polarization resistance, measured at various exposure intervals, decreased with the increase of molten salt exposure. The Nyquist plot consists of two semi-circles with an incomplete semi-circle at the lower frequency end, indicating the existence of three-time constants and formation of intermittent oxide film. The oxide films formed over the surface are characterized by Raman analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscope coupled with elemental analysis. The formation of Fe₃O₄, Cr₂O₃, iron hydroxide, W-oxides, and spinels are evidenced.